In commonly assigned U.S. Pat. No. 5,024,894, there is disclosed a novel method of applying to semiconductor wafer surfaces and the like a coating of a polymer metal complex to form thereon a corresponding insulating barrier metal oxide thin layer adhered to the wafer surface and non-reactive therewith. The layer is formed by firing at elevated temperatures in an air atmosphere to result in a smooth continuous uniform insulating coating or layer well-adhered to the substrate. The use of a dimethylformamide solvent for a copolymer of methacrylic acid and/vinyl acetate was therein described as dissolving a metal salt, such as a nitrate of magnesium, lanthanum, strontium, and other metal salts to provide, as by spin coating, a coated solution upon the desired substrates--in that case, a semiconductor wafer surface. The resulting micron thick film of polymer metal complex precursor thus applied to the substrate was then heated under an air atmosphere from room temperature to about 700.degree. C. for about 2 hours and then maintained at that temperature for another half hour, resulting in a smooth, continuous, pin-hole free insulating metal oxide layer of the order of 0.2 micron.
Such a technique has been found admirably suited to the coating of such semiconductor surfaces and the like as for buffer or similar purposes.
There are occasions, however, where the forming of similar high-temperature thermally stable metal oxide coatings on other types of substrates, including metal or other conducting substrate surfaces may be desired not only for some of the same reasons as described in said copending application, but also for very different functions and reasons. These include, for example, providing a hard and excellent wear-resistant coating, and/or a strongly insulating coating, and/or a high temperature thermally stable ceramic barrier, and/or for preventing rusting or other oxidation processes or attack by acids, while preventing the lifting of the coating that could otherwise permit attack of the substrate surface.
There are also instances where relatively conductive metal oxide coatings of uniform, pinhole free properties may be desired on insulating substrates, as of glass or the like, or on semiconducting substrates as in solar cell construction.
Underlying the present invention, indeed, is a discovery that rather critical modifications of the process described in said copending application may be instituted particularly to solve the above problems and it is to these purposes that the present invention is primarily directed.